Ah-kay,

There is no such thing as 2 phase 110V. It is single phase 120V. You don't get into 3 phase until you get to 240 and then it is usually a commercial or industrial application. Most houses have 240V service which is where you get the 240 for the clothes dryer but it is made up of 2 single phase 120 lines. You can get a sort of pseudo 209 V 3 phase for running larger ac units from a incoming 240v single phase line but I am not sure how they do it.

I have 2 Paloma gas tankless heaters and they are the best thing going. In 25 years I have put in an $11 diaphragm in each. They are expensive to buy but good over the long run if you have a big family. The only problem I had with them and teenagers is that once they find out that the hot water is endless they tend to use it. A 10 minute shower can turn into a one hour sauna.

I don't know how much electric will save because resistant heating from electricity is very expensive. Still it is a bit cheaper than having to keep 40+ gallons of water hot all the time in a standard electric tank type heater.